The first advertisement for the Bethlehem Spark Plug we can locate is from 2/9/1913 in the Houston Post. It is a full page ad, noting that the plug is "made from cold drawn steel and forged by the famous Bethlehem Steel Co." At the bottom of the ad stating "Manufactured by The Silvex Company, 60 Wall Street, NY." However, The Silvex Company began in Chicago, and was then purchased by Charles Schwab and moved to the old Haloyon Electric Light Company factory at West 4th St. in Bethlehem during June of 1912. They had been in operation in Chicago since the beginning of 1911. They specifically were set up to manufacture the spark plug and the "glad rag," both inventions of E. H. Schwab (Charles' brother).
In October of 1919, the newspapers report the name change (and massive factory expansion) from The Silvex Company to Bethlehem Spark Plug Company. E. H. Schwab is Pres. and E. B. Turn is Sec/Treas.
According to the 3/22/1925 edition of the Pittsburgh Press, Bethlehem Spark Plug Company merged with The Splitdorf Electrical Company of Newark, NJ. The new company name is the Bethlehem-Splitdorf Electric Company. The president of the new company will be M. W. Bartlett (from Splitdorf) and E. H. Schwab will serve as Chairman of the Board. Other board members include Charles Schwab, G. B. Alvord, C. E. Roraback, H. P. Ingels, Joseph Remick and Charles J. Splitdorf.
In June of 1928, they began manufacturing products for Thomas A. Edison, Inc. Soon thereafter, as reported in the 1929 edition of Moody's, Edison controlled the company.
A January, 1932 article in The Detroit Free Press seems to indicate that the Splitdorf-Bethlehem Electrical Co. is about to file for bankruptcy protection. However, other sources indicate that the company was split up among multiple Edison companies.